The invention relates to a manually actuable inhaler for pulverulent substances, in particular medicinal substances, in which, during the manual actuation, a defined discharge quantity from a substance storage quantity is apportioned out in a metering chamber upstream of a discharge passage for the purpose of airborne discharge from a mouthpiece opening at the end of the discharge passage, a piston which generates the discharge airstream, together with a cavity of its body portion, forming a substance storage chamber and the metering chamber, a reduced pressure which is generated during the return stroke of the piston opening toward the substance storage quantity, and furthermore the base of the metering chamber being formed by an air-permeable membrane.
DE-C 44 15 462 and EP 0 561 838 have disclosed application aids for pulverulent substances in the form of an inhaler which is conceived for emptying by a mouth sucking action. Depending on the user's constitution, the suction force generally differs extensively according to the particular individual.
WO 90/07351 has disclosed an inhaler in which the emptying of the metering chamber is effected by a pump/cylinder unit.
The administration of pulverulent substances, in particular of medicaments, requires not only a fine distribution in the transporting airstream but also that this airstream should always emerge with the same power, the latter as far as possible being stronger than that which a patient usually exerts or can exert by sucking. Only then can the pulverulent material reliably reach its intended destination. In this context, it is also necessary for the quantities to be precisely reproducible. This also requires, inter alia, that the pulverulent substance, i.e. the substance storage quantity, should not form a blockage. Furthermore, with regard to pump piston solutions, it is important to control the unpleasant effects of sudden bursts. Although it should be possible to apply a powerful transporting airstream, this airstream must not be excessive.